The present invention relates to a novel di-(meth)acrylic acid ester, a resin composition comprising the same and a coating agent for optical glass fiber for use in transmitting light.
Since the optical fibers have a large capacity of transmitting informations and do not relatively receive interferences from outside, the use thereof has been remarkably increased, particularly in the field of communication in the recent years. The optical fibers are generally made of glass, because they are used in the field of communication. However, since the glass fibers are frangible and chemically damaged by water vapour, they are easily broken and their handling is difficult. Accordingly, the optical glass fibers have hitherto been coated with a resinous material. As such a resinous coating material, epoxy resin, urethane resin or the like has hitherto been used, however, much time is needed to cure such a resin and therefore, the producibility of coated glass fibers is poor. Further, since cured resin lacks pliability, the coated glass fibers have the disadvantage of losing the transmitting property due to side pressure.
In recent years, in order to remove the above-mentioned disadvantage, a composition curable by ultraviolet rays containing urethane acrylate has been studied and examined, and a composition curable by ultraviolet rays for coating the optical glass fibers and a method for forming a coating film therefrom have been proposed, for instance, in Japanese Patent Application Laying-Open (KOKAI) No. 58-223638 (1983) and Canadian Patent No. 1198083.
Although the composition curable by ultraviolet rays, which has been used at present has the advantage of a high curing rate and also has the advantage that some desired properties can be reproduced easily and accurately, because of the large hygroscopic property this composition, a glass fiber coated with such a composition is apt to be spoiled by water and the coated glass fiber has the disadvantage that its physical properties change very much in the case where the temperature changes from -60.degree. to 80.degree. C. thereby causing an increase in transmission loss.
As a result of the present inventors' studies for solving the above-mentioned problems, the present inventors have found that a novel resin composition comprising novel di-(meth)acrylic acid ester has a high curing speed, provides a soft resin film of low hygroscopicity which has stable physical properties, which does not change between low and high temperature, and which has low glass-transition temperature and, novel resin composition is suitable for coating an optical glass fiber for transmitting light based on the present invention is these findings.